1. Field of the Invention
The present invention relates to a web electricity removing roller and, in particular, to a web electricity removing roller which removes the static electricity that appears on the surface of a web formed of paper, plastic sheet, or the like.
2. Description of the Related Art
Recently, in processes for manufacturing and machining webs which are formed of various kinds of plastics or the like, the web carrying speed has been increased to levels that have increased the possibility of static electricity. It is well known that static electricity gives rise to various kinds of obstacles in the respective processes for producing the webs. In other words, when the static electricity occurs in the web once, if the electric charges go over a predetermined value, then a spark discharge will be produced between the web and a carrying roller or other similar components. Occurrence of such discharge provides a very great problem. Especially, in steps of applying and drying an emulsion in manufacturing photo-sensitive materials, the webs may be defective due to such discharge.
In photographic paper or the like, there is included one which has a hydrophobic surface. That is, in the surface of the photographic paper, originally, a polymer film and a polymer are coated, so that the paper surface is hydrophobic. However, in order to be able to apply a photographic emulsion, especially, a gelatin silver halide emulsion, it is necessary to make the paper surface hydrophilic. For this reason, in the polymer-coated, photographic paper, a strong corona discharge is applied onto the surface of the paper to thereby activate the paper surface so that the surface has a hydrophilic nature.
However, after such corona discharge, static electric charges are present unevenly on the polymer surface. Because of this, it is impossible to coat the emulsion evenly. Therefore, it is necessary to remove the static electric charges from the surface of the photographic paper or to electrically charge the paper surface in an even manner before the emulsion is coated. This is why various kinds of electricity removing ways have been applied to such hydrophobic photographic paper and the like.
For example, there is disclosed by the present applicant an electricity removing method (Japanese Patent Application (Tokkai) No. 62-131500) of removing static electric charges from a web by guiding the web over an electricity removing roller which is formed by alternately combining a material to be positively chargeable by means of friction with respect to a charged web with a material to be negatively chargeable by means of such friction.
Also, the prior art electricity removing methods include: a method in which, in a route for carrying a support member before the emulsion is applied, there is provided a heating zone, where a blast of hot air is blown to the support member to heat the support member; a method in which there is provided an ultrared ray heating zone or a microwave heating oven, and a web is passed through such heating zone or oven so that the web can be heated radiatively or inductively; and, a method in which a carrying roller to be enageable with a web is heated electrically or by means of a blast of hot air or steam (see, Japanese Patent Application (Tokkai) No. 54-54020).
In addition, there is disclosed a method of removing electric charges from a film, in which negative and positive ions are generated from a corona-discharge-type electricity removing device using corona discharge.
Referring now to FIG. 6, there is shown an apparatus for removing corona discharge on the surface of a photographic paper by use of electrode rollers which are disclosed in Japanese Patent Publication (Tokkou) No. 49-37841. As shown in FIG. 6, a web 50, on which a corona discharge processing or an electricity removing processing is performed, is supplied from a roll 52. The web 50 is moved to an electrode roller 54, rollers 56, 58, an electrode roller 60 and discharge roller 62, sequentially in this order, that is, the web 50 is carried at a high speed between them for the above-mentioned processing.
The electrode roller 54 has a main body 55 which is formed of an electrically conductive material, and also has a rotational shaft 64 which is grounded. Upwardly of the electrode roller 54, there is provided a discharge electrode 68 which is connected to power supply source 66. In such structure, corona discharge can occur between the discharge electrode 68 and the electrode roller 54. The downstream electrode roller 60 has a main body 61 which is formed of an electrically conductive material and also has a rotational shaft 69 which is connected to another power supply source 71 in such a manner that a voltage of 500 to 50,000 volts can be applied.
Downwardly of the electrode roller 60, there is disposed a knife-shaped electrode 73 which is grounded. Due to this, a given voltage can be applied between the electrode roller 60 and the knife-shaped electrode 73.
In the above-mentioned structure, the web 50 is moved to and over the electrode rollers 54 and 60 at the speed of 15 to 180 m/min. (50 to 600 fpm) or greater before it is discharged. When the web 50 is moved to the electrode roller 54, the surface of the web 50 is processed by means of corona discharge, that is, the web surface is activated so that it becomes hydrophilic.
Also, when the web 50 is moved to the electrode roller 60, the uneven static charges on the surface thereof are processed so that the static charges are modified into an even state.
However, in the above-mentioned electricity removing methods by use of corona discharge, the voltage can be applied only between the knife-shaped electrode 73 and the electrode 60 and thus the time for neutralizing the web is limited. For this reason, if the delivering speed of the web 50 is increased, then the amount of ions supplied by means of the corona discharge will come short so that the static charges cannot be removed from the web surface in a satisfactory manner.